a. Field of the Invention
The present invention relates generally to the field of catheter ablation, and more particularly to an ablation catheter arrangement.
b. Background Art
Catheters have been in use for medical procedures for many years. Catheters can be used for medical procedures to examine, diagnose, and treat while positioned at a specific location within the body that is otherwise inaccessible without more invasive procedures. During these procedures a catheter is inserted into a vessel located near the surface of a human body and is guided to a specific location within the body for examination, diagnosis, and treatment. For example, one procedure often referred to as “catheter ablation” utilizes a catheter to convey an electrical stimulus to a selected location within the human body to create necrosis, which is commonly referred to as ablation of cardiac tissue. Another procedure oftentimes referred to as “mapping” utilizes a catheter with sensing electrodes to monitor various forms of electrical activity in the human body.
Catheters are used increasingly for medical procedures involving the human heart. As illustrated in FIG. 1, a typical human heart 10 includes a right ventricle 12, a right atrium 14, a left ventricle 16 and a left atrium 18. The right atrium is in fluid communication with the superior vena cava 20 and the inferior vena cava 22. The interatrial septum 24 separates the right atrium from the left atrium. The tricuspid valve 26 contained within the atrioventricular septum provides a fluid flow path between the right atrium with the right ventricle. On the inner wall of the right atrium where it is connected with the left atrium is a thin walled, recessed area, referred to as the fossa ovalis 28. Between the fossa ovalis and the tricuspid valve is the opening or ostium for the coronary sinus 30. The coronary sinus is the large epicardial vein which accommodates most of the venous blood which drains from the myocardium into the right atrium.
In a normal heart, contraction and relaxation of the heart muscle (myocardium) takes place in an organized fashion as electrochemical signals pass sequentially through the myocardium from the sinoatrial (SA) node (not shown) located in the right atrium to the atrialventricular (AV) node (not shown) and then along a well defined route which includes the His-Purkinje system into the left and right ventricles. Initial electric impulses are generated at the SA node and conducted to the AV node. The AV node lies near the ostium of the coronary sinus in the interatrial septum in the right atrium. The His-Purkinje system begins at the AV node and follows along the membranous interatrial septum toward the tricuspid valve 26 through the atrioventricular septum and into the membranous interventricular septum. At about the middle of the interventricular septum, the His-Purkinje system splits into right and left branches which straddle the summit of the muscular part of the interventricular septum.
Sometimes abnormal rhythms occur in the atrium which are referred to as atrial arrhythmia. Three of the most common arrhythmia are ectopic atrial tachycardia, atrial fibrillation and atrial flutter. Atrial fibrillation can result in significant patient discomfort and even death because of a number of associated problems, including the following: (1) an irregular heart rate, which causes a patient discomfort and anxiety, (2) loss of synchronous atrioventricular contractions which compromises cardiac hemodynamics resulting in varying levels of congestive heart failure, and (3) stasis of blood flow, which increases the vulnerability to thromboembolism. It is sometimes difficult to isolate a specific pathological cause for the atrial fibrillation although it is believed that the principal mechanism is one or a multitude of stray circuits within the left and/or right atrium. These circuits or stray electrical signals are believed to interfere with the normal electrochemical signals passing from the SA node to the AV node and into the ventricles. Efforts to alleviate these problems in the past have included significant usage of various drugs. In some circumstances drug therapy is ineffective and frequently is plagued with side effects such as dizziness, nausea, vision problems, and other difficulties.
An increasingly common medical procedure for the treatment of certain types of cardiac arrhythmia and atrial arrhythmia involves the ablation of tissue in the heart to cut off the path for stray or improper electrical signals. Such procedures are performed many times with an ablation catheter. Typically, the ablation catheter is inserted in an artery or vein in the leg, neck, or arm of the patient and threaded, sometimes with the aid of a guidewire or introducer, through the vessels until a distal tip of the ablation catheter reaches the desired location for the ablation procedure in the heart. The ablation catheters commonly used to perform these ablation procedures produce lesions and electrically isolate or render the tissue non-contractile at particular points in the cardiac tissue by physical contact of the cardiac tissue with an electrode of the ablation catheter and application of energy. The lesion partially or completely blocks the stray electrical signals to lessen or eliminate atrial fibrillations.
In some conventional ablation procedures, the ablation catheter includes a plurality of electrodes with a single distal electrode secured to the tip of the ablation catheter to produce small lesions wherever the tip contacts the tissue. To produce a linear lesion, the tip may be dragged slowly along the tissue during energy application. Increasingly, however, cardiac ablation procedures utilize multiple electrodes affixed to the catheter body to form multiple lesions.
One difficulty in obtaining an adequate ablation lesion using conventional ablation catheters is the constant movement of the heart, especially when there is an erratic or irregular heart beat. Another difficulty in obtaining an adequate ablation lesion is caused by the inability of conventional catheters to obtain and retain uniform contact with the cardiac tissue across the entire length of the ablation electrode surface. Without such continuous and uniform contact, any ablation lesions formed may not be adequate.
Moreover, effective ablation procedures are sometimes quite difficult because of the need for an extended linear lesion, sometimes as long as about three inches to five inches (approximately eight centimeters to twelve centimeters). To produce such a linear lesion of this length within an erratically beating heart is a difficult task. In some instances, stray electrical signals find a pathway down the pulmonary veins 32 and into the left atrium. In these instances, it may be desirable to produce a circumferential lesion at the ostium 34 to one or more of the pulmonary veins or within one or more of the pulmonary veins. The pulmonary veins may reach a circumference of up to about ten centimeters; thus, a ten centimeter circumferential lesion would be desirable to completely block stray signals from traveling down the pulmonary vein and into the left atrium.